Conventional molding materials such as polyethylene resin, polypropylene resin, nylon resin, polyester resin, ABS resin, polycarbonate resin, and polyacetal resin have been used in every field. Used products have been landfilled or incinerated, and, therefore, have put significant burden on the global environment, such as semipermanent stay in the ground or generation of carbon dioxide during incineration. In recent years, increased concentration of carbon dioxide, a greenhouse gas, in the atmosphere has been pointed out as a cause of global warming, and the movement for global-scale reduction of carbon dioxide emission is gathering momentum.
From the viewpoint of such environmental protection, utilization of biomass has received attention and substitution for fossil resource materials has been investigated. Also for molding materials, plant-derived resins, which allow reduction in use of fossil resources and reduction of carbon dioxide emission, has received attention. A representative plant-derived resin is an aliphatic polyester resin including a polylactic acid resin. However, the aliphatic polyester resin, compared to the existing petroleum resins, provides a molded product with reduced mechanical strength and heat resistance (heat distortion temperature), and further has a reduced thermal stability; therefore, aliphatic polyesters including polylactic acid have been of limited application. Further, reduction in thermal stability due to the use of an aliphatic polyester resin, because of its great effect on fluidity of the resin, has made it difficult to achieve stable molding processing conditions, and besides has imposed severe limitations on the molding method, the size of molding machine, and the like. Such characteristics of the aliphatic polyester resin make it difficult to maintain stable physical properties, leading to difficulty in mass production for market deployment, which has been a great obstacle to the future deployment as a more general-purpose resin.
To solve the problems of the aliphatic polyester resin mentioned above, various improvements have hitherto been made. As a method for the improvement, polymer alloy with the existing resin described above and addition of modifiers have been actively carried out.
Patent Document 1 discloses improving mechanical strength and thermal stability by adding a phosphoric acid-based compound to an alloy of a rubber-toughened styrene-based resin, a polycarbonate resin, and a polyester resin and describes the thermal stability of the polycarbonate resin, but does not describe a thermal stability technique for the polyester resin. Thus, the improvement in thermal stability of an alloy of the rubber-toughened styrene-based resin and the polyester resin required further improvement.
Patent Document 2 discloses that both mechanical strength and heat resistance can be improved by alloying an aliphatic polyester resin with a rubber-toughened styrene-based resin and an acrylic-based resin, and further adding dicarboxylic anhydride; however, the thermal stability was poorly investigated, and further improvement was required. Further, it describes that it is preferable to use maleic anhydride or succinic anhydride as dicarboxylic anhydride, but an irritating odor emanates during compounding of the aliphatic polyester resin, the rubber-toughened styrene-based resin, and the acrylic-based resin and during subsequent molding processing, which has been problematic in terms of safety and hygiene considering the influence on human health during the production.